The present invention relates to shaped charge explosive devices, and in particular, to a method and device for controlling the final shape of an explosively formed penetrator.
In the past, explosively formed penetrator devices have been limited in the sense that the final penetrator shape could only be controlled within the range of adjustable parameters concerning the explosive geometry, the liner geometry, and explosive initiation scheme. However, penetrators have been formed with shapes conforming roughly to spheroids and rods. Even there, the dynamic forming process created shot-to-shot variations in penetrator shapes together with gross imperfections. In reality, penetrator material was seldom disposed in compact form about the symmetry axis. Thus, hollow portions and mass variations existed along the penetrator length in the rod cause, and about a center point in the spheroidal case.
Also, some success has been obtained in producing aerodynamically stable penetrator shapes i.e., those formed with a drag flare. However, offsetting penalties, such as a rod length reduction and therefore penetration loss, have been experienced. Examples of rods formed with flares exhibited not only reduced length but also static margins which were barely acceptable.
The inability to produce further changes in mass distribution along the penetrator length also limits the penetration power of the penetrator. For certain penetration applications, a hollow or tubular penetrator shape is desired. Hollow penetrators have been formed by reducing the severity of liner flow toward the symmetry axis, the final cavity size being dependent upon the material's ability to absorb the energy involved to prevent further flow toward the axis. Since this is an asymptotic process, wide variations in the tube wall radius along the penetrator length resulted.
For solid body penetrators, more control of the velocity gradient and mass distribution over the penetrator length is desired. Limitations in explosives/metal geometry, and the nature of the dynamic forming process create wide variations in these parameters. Reducing the velocity gradient is not a solution as it has the effect of producing reduced final penetrator length. Increasing penetrator length using high velocity gradients along the penetrator length causes excessive stretching which results in penetrator breakup.